Don Terrill’s Speed-Talk

I've asked this question buried in some other thread and was referred to some tech papers (Harvey Crane's among others) etc. on how this plays out but never got a definitive answer (if one exists).
I figured I'd make a new post asking the question directly.

Somewhat specifically, I've two hydraulic roller profiles to choose from. The application is endurance/WOT for minutes at a time with a Gen 1 SBC. RPM is 6500 maximum. Also some drag racing and general all around driving but the endurance aspect I'll emphasize as I think that would indicate that a lobe that's too intense is going to cause maintenance and longevity issues. Certainly more so than modest drag racing would.

I'm not looking for a recommendation on a cam spec as many here (and elsewhere) have already done that so the basics are set. And thanks.
Let's also say that the rest of the valvetrain is up it. Details if needed. Suggestions welcomed. Rockers arms are finalized at 1.6.

Seat to seat is centred around 284.


It's plain to see which lobe is faster and with that comes the benefits associated with that. But is the 2nd profile too much for WOT down a Nevada (or Nebraska) highway?

I would check with the cam company on that higher intensity lobe.
They should know if 1.6 RR were in the design parameters.
Some lobes are designed to be RR specific or tolerable.
With a solid I would go for it, but a Hyd might not like the little extra the 1.6 RR puts on it.
A good Cam Mfg should give you the correct answer. Don't believe the Helpers or just a salesman.
Get someone familiar with designs.
Good luck

What I have learned in those numbers don't tell you really how it's going to impact the valvetrain. You need someone who knows what they're looking at to see the derivatives (Cam Doctor level at least). Plenty of old school, low intensity cams out there that actually have crazy acceleration and jerk numbers.

Then as Adger said, multiply that through the rocker. Some might be okay at 1.6 and be a mess anything beyond that.

edit

Adger Smith wrote: ↑Sat Oct 09, 2021 3:10 pm I would check with the cam company on that higher intensity lobe.
They should know if 1.6 RR were in the design parameters.
Some lobes are designed to be RR specific or tolerable.
With a solid I would go for it, but a Hyd might not like the little extra the 1.6 RR puts on it.
A good Cam Mfg should give you the correct answer. Don't believe the Helpers or just a salesman.
Get someone familiar with designs.
Good luck

This is part of the plan.
I had read Mike Jones explanation of the pros and cons of increased ratio on a slower lobe vs the other way around.
And in the direction of my original question, I see that comes into play as well.
I will say though that I have something invested in my current 1.6 rockers and want to use them going forward. How that shakes out remains to be seen.

hoffman900 wrote: ↑Sat Oct 09, 2021 3:14 pm What I have learned in those numbers don't tell you really how it's going to impact the valvetrain. You need someone who knows what they're looking at to see the derivatives (Cam Doctor level at least). Plenty of old school, low intensity cams out there that actually have crazy acceleration and jerk numbers.

Then as Adger said, multiply that through the rocker. Some might be okay at 1.6 and be a mess anything beyond that.

Absolutely. I've seen some Spintron data with regards to the valve springs. It prompted a move to COMPs beehive springs (keep in mind this was 20 years ago). The thinking that along with lighter tool steel retainers it would give some headroom and stability.
Fast forward to today and I'm still asking questions.

Kevin,
The Cam Pro Plus program (Cam Dr.) will give a guy a good education in lobes and RR function, esp if you have developed a large data base.
Basic design parameters are the starting point.
Why and What was the original design purpose and where do the changes take you???
Do you find broken or stressed part or more power.
Do the changes take it too far or far enough?

Looking at Cam Dr. I'm not sure if it's the stuff of the hobbyist. Which is what I am.
That doesn't mean I don't appreciate all of the science. I'll look into it further.
That said, one excellent explanation with respect to ratio vs lobe lift I've come across was posted by CamKing .

CamKing wrote: ↑Mon Mar 14, 2016 10:46 am

KnightEngines wrote: Ignoring lobe design specifics which option will result in the most stable valve train & best lifter life?

As long as you can keep the rocker geometry in check with the higher ratio, you will have better valvetrain stability and longevity.
In both cases, if done correctly, the acceleration, velocity, and travel of the valve, retainer and spring will be the same.
With low lobe lift, and higher ratio, you reduce the acceleration, velocity, and travel of the lifter and pushrod. The lower lobe lift allows for a bigger base circle. The lower lifter velocity and larger base circle cause less side loading on the roller lifters.
The problem with the higher ratio is that the spring pressure is multiplied by that higher ratio, and can cause more pushrod flex, and lifter wear. It can also cause increased bleed-down with hydr lifters. The good thing is, since the acceleration of the lifter and pushrod isn't as high, you don't need as much spring pressure to control it, so you can reduce your spring rate.

The issue of base circle is addressed and that's of interest to me as well.
Knight Engines asked my question in a different way.

KnightEngines wrote: Ignoring lobe design specifics which option will result in the most stable valve train & best lifter life?

I'll say lifter life and stability equates to overall durability.

skinny z wrote: ↑Sat Oct 09, 2021 5:13 pm Looking at Cam Dr. I'm not sure if it's the stuff of the hobbyist. Which is what I am.
That doesn't mean I don't appreciate all of the science. I'll look into it further.
That said, one excellent explanation with respect to ratio vs lobe lift I've come across was posted by CamKing .

CamKing wrote: ↑Mon Mar 14, 2016 10:46 am

KnightEngines wrote: Ignoring lobe design specifics which option will result in the most stable valve train & best lifter life?

As long as you can keep the rocker geometry in check with the higher ratio, you will have better valvetrain stability and longevity.
In both cases, if done correctly, the acceleration, velocity, and travel of the valve, retainer and spring will be the same.
With low lobe lift, and higher ratio, you reduce the acceleration, velocity, and travel of the lifter and pushrod. The lower lobe lift allows for a bigger base circle. The lower lifter velocity and larger base circle cause less side loading on the roller lifters.
The problem with the higher ratio is that the spring pressure is multiplied by that higher ratio, and can cause more pushrod flex, and lifter wear. It can also cause increased bleed-down with hydr lifters. The good thing is, since the acceleration of the lifter and pushrod isn't as high, you don't need as much spring pressure to control it, so you can reduce your spring rate.

The issue of base circle is addressed and that's of interest to me as well.
Knight Engines asked my question in a different way.

KnightEngines wrote: Ignoring lobe design specifics which option will result in the most stable valve train & best lifter life?

I'll say lifter life and stability equates to overall durability.

Anything to preserve as much base circle to me made the most sense. That means smaller lobes and more rocker ratio, if rules allow.

I know the CamProPlus measurement and looking at the derivative charts is advanced, but it's the only way to answer your question accurately. You don't need to be a math wizard to see which one has lower peak acceleration and where, and has the lowest jerk value.

hoffman900 wrote: ↑Sun Oct 10, 2021 11:14 am

I know the CamProPlus measurement and looking at the derivative charts is advanced, but it's the only way to answer your question accurately. You don't need to be a math wizard to see which one has lower peak acceleration and where, and has the lowest jerk value.

Am I missing something with CamPro?
When I checked it out it appeared to me to be equipment for shop or in-house measurements.



I was anticipating some kind of software bundle like DynoSim or Torque Master (although those two aren't lobe profile specific just examples).
Equipment like that posted above is above this enthusiast level. But I'd like to see all of the data that's churned out.

hoffman900 wrote: ↑Sat Oct 09, 2021 3:14 pm You need someone who knows what they're looking at...

Still agreed on this.
Those profiles posted are from the same manufacturer's catalog and they have plenty of representation here at ST.

Kevin,
That equipment measures the actual cam lobe. It will export that data in S96 format. Instead of just giving Dynomation some information about your cam, Dynomation can import the S96 file to get what ever it wants / needs.

Stan

That's what I figured Stan.
I can't say that I'm one to integrate that level of equipment into my shop in as much as I'd like to. The data would be interesting though.
Working in a machine shop/ manufacturing facility, I've access to all kinds of measuring equipment like our several CMM's but they're not camshaft friendly!

Maybe Cam King uses Cam Dr. and has all of that info...I'm sure he has all of that and more (those are his lobes too).

From my spintron experience ( we own 2 ) the problem is EVERYTHING affects everything in a dynamic state. Sim's can help with understanding but real world most always shows unwanted compliance or deflection that was never figured into a sim program. The results very AND are always changing with rpm. Intensity number can be misleading because of where it is on the lobe. We have moved it up and down 5-10* and kept the same amount and completely changed the valve motion and stability. Our facebook page 3V Performance has some cool 11,000+ rpm spintron videos for those who have not seen one run.

I could've sworn Mike said you're usually better off with lobe lift and less rocker but that may have been solely for the sake of keeping the plunger happy. Everything has it's little happy zone though so I'm sure at some point, side load becomes a bigger issue than plunger stability.

I'm curious to see how this plays out.